Electric arc furnace steelmaking is in the ascendant in iron and steel production enterprises. At present, among the three methods of open hearth, converter, and electric arc furnace steelmaking, the proportion of electric furnace steel reaches about 30%. Electric arc furnace steelmaking uses graphite electrodes as conductive materials. The consumption of graphite electrodes in electric arc furnace steelmaking depends not only on the quality of the electrodes, but also on the level of steelmaking operations and management. Now, we will analyze the usage problems accumulated by our factory's graphite electrode user service for many years, in order to benefit the operation of graphite electrode in electric arc furnace steelmaking.

01

What are the main factors affecting graphite electrode consumption in electric arc furnace steelmaking?

Mainly include: (1) Filling amount and feeding method. (2) Feeding time and power-off time. (3) Smelting cycle. (4) Exhaust gas emission and dust removal system. (5) Electrode adjustment quality. (6) Load regulation quality. (7) Oxygen blowing operation. (8) The quality of electrode connection. (9) The quality of the electrode connector body. (10) Electrode joint hole and joint processing accurac

02

What matters should be paid attention to in the storage of graphite electrodes in steel mills?

The electrodes and connectors should be stored on a clean concrete floor to prevent the electrodes from being damaged or sticking to soil; do not remove the packaging for the electrodes that are not used temporarily to prevent dust and debris from falling on the connector threads or the electrode end face and the inner thread of the electrode hole superior. Electrodes should be neatly stored in the warehouse, and both ends of the electrode stack should be padded to prevent slipping. The stack height of the electrodes should generally not exceed two meters. The stored electrodes should be protected from rain and moisture to avoid cracks and accelerated oxidation of the electrodes during steelmaking. Do not store the electrode connector near high temperature to prevent the connector plug from melting and overflowing.

03

How to avoid electrode breaking and tripping during steelmaking?

During the steelmaking process, the following measures can be taken to effectively avoid electrode breakage and tripping: (1) The electrode phase sequence is correct, counterclockwise. (2) The scrap steel is evenly distributed in the steel furnace, and large pieces of scrap steel should be placed at the bottom of the furnace as much as possible. (3) Avoid non-conductive materials in scrap steel. (4) The electrode column is aligned with the furnace top hole, and the electrode column is parallel. The furnace top hole wall should be cleaned frequently to avoid the accumulation of residual steel slag and force the electrode to be broken. (5) Keep the electric furnace tilting system in good condition and keep the electric furnace tilting stable. (6) Avoid clamping the electrode holder at the electrode connection and electrode joint hole. (7) Choose joints with high strength and high processing accuracy. (8) The torque applied when the electrodes are connected should be appropriate. (9) Before and during the electrode connection, prevent the electrode hole thread and connector thread from mechanical damage. (10) Prevent steel slag or foreign objects from being embedded in the electrode hole and joint to affect the screw connection.

04

When steel mills use graphite electrodes, what should be paid attention to during crane lifting?

Regardless of whether the electrode is transported by a forklift or a crane, it must be carefully operated. During the lifting of the electrode, damage to the electrode end and thread will cause serious problems to the use of the electrode, especially the protection of the threaded hole and the thread of the connector. When lifting the electrode, there must be a protective pad to avoid damaging the electrode end surface and the thread of the connector.

05

How to connect the electrodes correctly?

When connecting, use compressed air to blow clean the inside of the electrode hole, the electrode end face and the joint. There should be no dust and foreign objects embedded. The connection should be kept clean and flat. When the two electrodes are screwed in to a certain extent (the gap is about 10mm), then Blow once with compressed air, and then tighten the electrode with torque pliers. The torque applied during tightening should be appropriate. If there is a gap in the connection after tightening, it must be withdrawn and reconnected until there is no gap.

06

About the correct clamping position of the electrode holder

The electrode holder cannot be clamped between the electrode connection and the electrode threaded hole. It should be clamped between the white wires at both ends of the electrode. At the same time, before the electrode is clamped by the holder, the surface of the electrode and the holder must be clamped with compressed air. Blow clean to ensure good conduction of current and heat flow between the electrode and the holder, prevent arcing from causing damage to the holder, thereby prolonging the life of the holder.

07

What are the measures to reduce electrode oxidation consumption in electric arc furnace steelmaking?

The main reduction measures are: (1) Reduce the oxidation consumption of the electrode perimeter, strengthen the sealing of the furnace, and reduce the air intrusion into the furnace; minimize the exposure time of the red hot electrode outside the furnace, and standardize the oxygen blowing operation. (2) For the smelting furnace, if conditions permit, the electrode adopts spray cooling technology, which can effectively reduce the oxidation consumption of the electrode side. (3) The steel plant sprays anti-oxidant substances on the surface of the electrode, or the electrode manufacturer adopts the anti-oxidant dipping treatment technology before the electrode leaves the factory to improve the anti-oxidation performance of the electrode body.

08

How does the electrode phase sequence affect the use of electrodes?

The positive electrode phase sequence during electric arc furnace steelmaking has a significant impact on the tripping and breaking of the electrode during use. If the electrode phase sequence is clockwise, the electrode will loosen after being energized for a period of time during use, which will easily cause the electrode to loosen. Or the connector is broken, the correct electrode phase sequence should be counterclockwise, so that the electrode will be more and more tightly joined during use.

09

Why is the phase electrode required to be parallel and centered with the top hole of the furnace cover during electric arc furnace steelmaking?

When the electrode column and the top hole of the furnace cover are dealt with, the electrode column should avoid friction with the furnace cover, otherwise the furnace cover will squeeze the electrode when it is raised and lowered. For the AC furnace, the three-phase electrode column should be kept parallel as much as possible .

10

How to apply torque when the electrode is screwed?

The torque applied when the electrode is screwed must be appropriate, and the operation must be inertial. Too small a torque will cause the joint to loosen thermally, and too much torque will cause the electrode joint hole to crack. When screwing, use a special electrode screwing tool. Do not screw. Too tight and too loose. If there is a gap in the end face contact after tightening, it must be removed and cleaned before re-spinning.

11

Why is graphite spreader better than metal spreader?

Although the metal sling is durable and not easy to be damaged, the thermal expansion of the metal sling is easy to rupture the electrode hole when it is heated during use. At the same time, the thread in the electrode hole is easily damaged when the metal sling is taken, causing a large area of the thread in the hole to be scraped. The graphite spreader has the same thermal expansion and hardness as the electrode, so the above-mentioned poor use will not occur. However, the graphite spreader has a short service life and is easy to be damaged. If serious damage is found, It should be replaced in time.

12

How to choose the correct electrode in electric arc furnace steelmaking?

According to the design characteristics of the electric arc furnace, the electrode that meets the production of the electric arc furnace is selected reasonably, and the product with the best cost performance is selected. It is very necessary to carefully select the electrode suitable for each furnace. The special performance of the steelmaking furnace, the feeding method, the maximum current intensity, the length of the electrode column under the holder, the distance between the side wall of the furnace and the electrode circumference, etc. It is a factor that must be considered when choosing an electrode for an electric arc furnace

13

What effect does the electrical resistivity performance have on the use of electrodes in steelmaking?

The resistivity of a graphite electrode is a physical index that reflects the electrical conductivity of the electrode. It is related to the manufacturing process of the electrode. The country has qualitatively specified values for the resistivity of graphite electrodes of different specifications. Generally speaking, steel plants choose certain specifications When the electrode is used, it must be selected within the resistivity range specified by the national metallurgical standards. Too high resistivity will cause the electrode to become red and hot when it is energized, and increase the electrode oxidation consumption.

14

What effect does the volume density performance have on the use of electrodes in steelmaking?

The volume density of the graphite electrode reflects the compact state of the electrode, which is closely related to the manufacturing process of the electrode. The country has specified values for the volume density of graphite electrodes of different specifications and varieties. Products with low bulk density indicate that the overall structure of the product has higher porosity, and the oxidation rate of the product is faster when the product is high temperature, which will easily cause the electrode consumption to increase. Generally speaking, when the steel plant chooses the electrode, the electrode bulk density is better within the specified value. , But the higher the bulk density is not the better, because some electrodes with too high bulk density are sometimes prone to surface peeling, lumps and cracks during steelmaking due to poor thermal shock resistance, which will adversely affect steelmaking.

15

When steel mills use graphite electrodes, why should they prevent multiple products from being mixed?

Graphite electrodes used in steel mills are often supplied by multiple manufacturing companies. When multiple products are used in steelmaking, it will not only make it difficult for steel mills to calculate the consumption of a single product, but also because of the different raw materials and manufacturing processes used by each manufacturer. , The physical and chemical properties and processing tolerances of electrodes and joints of various manufacturers have certain differences. Therefore, the matching tolerances produced during mixed use can easily cause the electrodes to fall off and break. The correct way to use is to use the products of one manufacturer alone, and then connect to the products of another manufacturer after the end. It is necessary to reduce the number of electrode replacements using different manufacturers. Electrodes from the same manufacturer should use the connectors provided by the same manufacturer to prevent mixing.

16

What are the characteristics of needle coke?

Needle coke is a high-quality carbon raw material, divided into coal-based and oil-based. Its surface has obvious strip lines, and most of them are long needle-shaped fragments when broken. The fibrous structure can be observed under a microscope. Hence it is called needle coke. Needle coke is easy to graphitize at a high temperature above 2000 degrees. Graphite electrodes made with it not only have low electrical resistivity, high bulk density, and low thermal expansion coefficient, it is suitable for the production of ultra-high power electrodes and high power Essential material for electrodes. The price of needle coke is much more expensive than that of ordinary coke, and is currently about 5-8 times higher.

17

Will the dust collection system on the electric arc furnace affect the consumption of electrodes?

The fan used in the dust collection system generates a certain negative pressure during work, which increases the air flow rate around the red hot electrode during steelmaking, which also increases the oxidation consumption of the electrode. During steelmaking, a well-adjusted dust collection system, namely Maintain a good working environment and stabilize the consumption of electrodes.

18

How to avoid the increase of electrode consumption during steelmaking?

To avoid the increase of electrode consumption during steelmaking, the following should be done: (1) Maintain a good power supply state, and deliver electricity within the range of the electrode's allowable current intensity according to the design requirements of the electric furnace. (2) Prevent the arc starting point from being immersed in the molten pool. (3) Prevent the electrode from being immersed in molten steel to increase carbon. (4) If conditions permit, the electrode adopts spray cooling technology. (5) Set up the correct exhaust emission system. (6) Use the correct oxygen blowing system.

19

How long does the production cycle of graphite electrodes take?

The production process of a batch of ultra-high-power or high-power graphite electrodes and the corresponding time are as follows: electrode pressure type (3 days)-roasting (25 days)-impregnation (4 days)-re-roasting (15 days) )-Graphitization (10 days)-Machining, quality inspection (2 days)-Finished product packaging and delivery (1 day), that is, from feeding to product shipment, the fastest cycle of non-stop production is also 60 However, since the production of electrode joints requires more two-immersion and three-baking treatment than electrodes, the fastest production cycle is 90 days.

20

What are the characteristics of electrodes produced by tandem graphitization furnaces?

The development direction of graphitization furnace is internal heat tandem graphitization furnace. Because the current density of the series connection column is the same, the electrode resistivity difference is very small; secondly, the resistivity at both ends of the inner string graphitized product is slightly lower than the middle part (the Acheson furnace graphitized product has a higher resistivity at both ends than the middle part). It is beneficial to reduce the resistance of the connection when the user uses it, and alleviate the overheating and redness of the joint connection. Therefore, the electrode quality uniformity produced by the tandem graphitization furnace is better than that of the Acheson furnace, and it is more suitable for the production of electric arc furnace steelmaking. Require.

21

Why is the quality of electrode joints important in electric arc furnace steelmaking?

The joint plays a key role in the connection of the electrode steelmaking. The quality of the joint is directly related to the use of the electrode in the electric furnace steelmaking. Problems can also arise. According to relevant data, in electric furnace steelmaking, more than 80% of electrode accidents are caused by broken joints and loose tripping. Therefore, the selection of high-quality electrode joints is a guarantee condition for the normal use of electric furnace steelmaking electrodes.

22

Which quality indicators of graphite electrode (joint) products have an impact on electric furnace steelmaking?

(1) Quality indicators such as the bulk density, resistivity, strength, elastic modulus and thermal expansion coefficient of the electrode. (2) Quality indicators such as bulk density, resistivity, strength, elastic modulus and thermal expansion coefficient of the joint. (3) The machining accuracy of electrodes and joints. No matter how good the quality of electrodes and joints is, there is no good machining accuracy (mainly refers to the cooperation of electrodes and joints), and the use effect is not good. (4) The internal structural quality of electrodes and joints requires that there are no cracks that cause hidden dangers in use.

23

What are the consequences of severe oxidation of the electrode end surface at the upper end of the electrode holder?

During steelmaking in the smelting furnace, the scrap is burned in the furnace. At the same time, due to the oxygen blowing in the furnace, the height of the flame column is often higher than the electrode end surface at the upper end of the holder, which is easy to oxidize the electrode end surface. If the oxidation is serious, the electrode end surface will be deformed. The plane becomes an inclined plane. When a new electrode is connected to the upper end, the end surface of the lower electrode is oxidized and deformed and cannot make good contact with the new electrode. The electrode gap is large, which may easily cause oxidation and breakage of the internal joint. Without changing the steelmaking conditions, the best preventive measure is to install a protective cover on the electrode end face at the upper end of the holder to block flame and air to protect the electrode end face.